Foreign matter inspection apparatus and foreign matter inspection method

ABSTRACT

A foreign-matter inspection apparatus is implemented which allows the stable detection sensitivity to be maintained. A laser beam emitted from a laser apparatus is applied to a beam irradiation sample via an irradiation unit and a mirror. Then, the laser beam is captured into a beam-capturing camera via an image-forming lens and a beam-direction switching mirror. Based on the captured beam image, an image computational processing unit judges inclination of the laser beam, then adjusting the irradiation unit thereby to correct the inclination of the laser beam. Also, the beam is captured into the beam-capturing camera in specified number-of-times while focus of the laser beam is being changed by an arbitrary amount by the irradiation unit. Based on the captured beam, the focus of the laser beam is corrected by adjusting the irradiation unit.

BACKGROUND OF THE INVENTION

The present invention relates to a foreign-matter inspection apparatusfor detecting a foreign matter, scratch, defect, dirt, and the likeexisting on the surface of a inspection target such as a semiconductorwafer.

As disclosed in JP-A-2005-283190, in an apparatus for detecting aforeign matter (including scratch, defect, dirt, and the like) existingon the surface of a inspection target, e.g., a semiconductor wafer, theforeign matter is detected as follows: The surface of the semiconductorwafer is irradiated with laser light. Next, reflected light or scatteredlight is detected from the surface of the semiconductor wafer, therebydetecting the foreign matter existing on the surface thereof.

The laser beam, with which the surface of the semiconductor wafer isirradiated, is of a transversely-long elliptic shape. Moreover, the beamis emitted and applied thereto in a manner of being parallel to acamera. By maintaining this parallel state, i.e., by executing the beamirradiation in the same state always, it becomes possible to stabilizeforeign-matter detection sensitivity of the foreign-matter inspectionapparatus.

As described above, in the foreign-matter inspection apparatus, theforeign-matter detection sensitivity is stabilized by irradiating thesurface of a inspection target with the laser light in the same statealways.

In some cases, however, an assembly error occurs in the structure insidethe foreign-matter inspection apparatus due to a reason such astime-lapse change. In this case, the beam with which the surface of thesemiconductor wafer is irradiated cannot maintain the parallel statewith respect to the camera. As a result, it turns out that the beam isemitted and applied to the semiconductor wafer in a state where the beambecomes oblique to the camera or the beam is not focused. When the beamcannot maintain the parallel state or the like with respect to thecamera, the foreign-matter detection accuracy is dropped, and thus thesensitivity becomes lowered.

In the conventional technology, no consideration has been given to thispoint. Accordingly, there has existed a possibility that theforeign-matter detection sensitivity becomes unstable.

SUMMARY OF THE INVENTION

It is an object of the present invention to provide a foreign-matterinspection apparatus and foreign-matter inspection method which allowsthe stable detection sensitivity to be maintained.

There is provided a foreign-matter inspection method of the presentinvention for detecting a foreign matter by irradiating surface of aflat-plane-shaped inspection target with an ellipse-shaped laser beam,the foreign matter including scratch, defect, and dirt, and existing onthe surface of the inspection target, the foreign-matter inspectionmethod including the steps of irradiating the surface of a flat-planeportion of the beam irradiation sample with the generated laser beam,the beam irradiation sample being fixed to an inspection stage for theinspection target, photographing the laser beam by using a photographingunit, the laser beam being reflected from the beam irradiation sample,forming a beam image based on the laser beam photographed, calculating,from the beam image, an inclination angle of the laser beam's major axisor minor axis relative to a constant reference line, and correcting theinclination angle of the laser beam.

There is also provided a foreign-matter inspection method of the presentinvention, the foreign-matter inspection method including the steps ofirradiating a flat-plane portion of a beam irradiation sample with agenerated laser beam while changing focus width of a laser-beam-widthfocus adjustment unit and via the laser-beam-width focus adjustmentunit, the beam irradiation sample being fixed to an inspection stage,forming a beam image based on the laser beam reflected from the beamirradiation sample, calculating, from the beam image, the width of thelaser beam with which the flat-plane portion is irradiated, and setting,based on the width, the focus width of the laser-beam-width focusadjustment unit at a focus width in a case where the width of the laserbeam with which the flat-plane portion is to be irradiated is thenarrowest width.

There is provided a foreign-matter inspection apparatus of the presentinvention for detecting a foreign matter by irradiating surface of aflat-plane-shaped inspection target with an ellipse-shaped laser beam,the foreign matter including scratch, defect, and dirt, and existing onthe surface of the inspection target, the foreign-matter inspectionapparatus including a laser-beam generation unit, an inclination-angleadjustment unit for adjusting an inclination angle of the laser beam'smajor axis or minor axis relative to a constant reference line, aflat-plane portion irradiated with the laser beam via theinclination-angle adjustment unit, the beam irradiation sample fixed toan inspection stage, a photographing unit for photographing the laserbeam reflected from the beam irradiation sample, an image formation unitfor forming an image of the laser beam photographed, and a computationalcontrol unit for calculating, from the laser-beam image, the inclinationangle of the laser beam's major axis or minor axis relative to theconstant reference line, and correcting the inclination angle of thelaser beam relative to the constant reference line by activating theinclination-angle adjustment unit.

There is also provided a foreign-matter inspection apparatus including alaser-beam-width focus adjustment unit for adjusting width of a laserbeam generated from a laser-beam generation unit, a flat-plane portionirradiated with the laser beam via the laser-beam-width focus adjustmentunit, a beam irradiation sample fixed to an inspection stage, aphotographing unit for photographing the laser beam reflected from thebeam irradiation sample, an image formation unit for forming a beamimage based on the laser beam photographed, and a computational controlunit for causing the laser beam to be generated from the laser-beamgeneration unit, irradiating the flat-plane portion of the beamirradiation sample with the generated laser beam while changing focuswidth of the laser-beam-width focus adjustment unit and via thelaser-beam-width focus adjustment unit, calculating, from the beamimage, the width of the laser beam with which the flat-plane portion isirradiated, the beam image being formed based on the laser beamphotographed by the photographing unit, and setting, based on thecalculated width of the laser beam, the focus width of thelaser-beam-width focus adjustment unit at a focus width in a case wherethe width of the laser beam with which the flat-plane portion is to beirradiated is the narrowest width.

According to the present invention, a foreign-matter inspectionapparatus and foreign-matter inspection method which allows the stabledetection sensitivity to be maintained.

Other objects, features and advantages of the invention will becomeapparent from the following description of the embodiments of theinvention taken in conjunction with the accompanying drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a schematic configuration diagram of a foreign-matterinspection apparatus which is an embodiment of the present invention;

FIG. 2 is a diagram for illustrating an optical portion of theirradiation unit illustrated in FIG. 1;

FIG. 3 is an explanatory diagram for explaining the beam irradiationsample illustrated in FIG. 1;

FIG. 4 is an operation-control functional block diagram of inclinationcorrection and focus correction for the laser beam;

FIG. 5 is an inclination-correction operation flowchart of the laserbeam in the embodiment of the present invention;

FIG. 6A is a diagram for illustrating the inclination of the laser beamin the embodiment of the present invention;

FIG. 6B is a diagram for illustrating the inclination of the laser beamin the embodiment of the present invention, using a numerical valuediagram;

FIG. 7A is a diagram for illustrating a case where the inclination ofthe laser beam in the embodiment of the present invention is corrected;

FIG. 7B is a diagram for illustrating the case where the inclination ofthe laser beam in the embodiment of the present invention is corrected,using a numerical value diagram;

FIG. 8 is a focus-correction operation flowchart of the laser beam inthe embodiment of the present invention;

FIG. 9 is a diagram for illustrating width of the laser beam in theembodiment of the present invention, and a diagram for illustrating thewidth using a numerical value diagram;

FIG. 10 is a diagram for illustrating a screen display exampleindicating that carry-out of the sensitivity automatic adjustment isunderway in the embodiment of the present invention;

FIG. 11 is a diagram for illustrating a screen display exampleindicating termination of the sensitivity automatic adjustment in theembodiment of the present invention, and its result in the embodiment ofthe present invention;

FIG. 12 is a diagram for illustrating an example of a result log fileafter the termination of the sensitivity automatic adjustment in theembodiment of the present invention;

FIG. 13 is a diagram for illustrating an example of an operationflowchart in a case where the laser-beam inclination correction and thelaser-beam focus correction are continuously executed; and

FIG. 14 is a diagram for illustrating another example of the operationflowchart in the case where the laser-beam inclination correction andthe laser-beam focus correction are continuously executed.

DESCRIPTION OF THE INVENTION

Hereinafter, referring to the accompanying drawings, the explanationwill be given below concerning embodiments of the present invention.

FIG. 1 is a schematic configuration diagram of a foreign-matterinspection apparatus which is an embodiment of the present invention.This is the diagram where the present invention is applied to theforeign-matter inspection apparatus for inspecting a foreign matterexisting on the surface of a semiconductor wafer. Incidentally,excluding components such as cover for covering the foreign-matterinspection apparatus, base, and operating table, FIG. 1 illustrates theschematic configuration extending from a laser apparatus to a stage ofcapturing a beam image. Additionally, a foreign matter, scratch, defect,dirt, and the like are generically referred to and defined as “foreignmatter”.

In FIG. 1, the foreign-matter inspection apparatus includes the laserapparatus 10, an irradiation unit 20, a beam-irradiation-angle switchingmirror 30, a beam irradiation sample 40, an image-forming lens 50, abeam-direction switching mirror 60, a beam-capturing camera 70, and aflat-plane-shaped inspection stage 80. A semiconductor wafer 90, i.e., aflat-plane-shaped inspection target, is disposed on the inspection stage80. A foreign matter or the like existing on the surface of thissemiconductor wafer 90 is detected.

Here, the beam irradiation sample 40 is fixed to the inspection stage80.

A foreign-matter inspection operation is performed as follows: Theinspection stage 80 is scanned in the X and Y directions whileirradiating the semiconductor wafer 90 on the inspection stage 80 with alight beam emitted from the laser apparatus 10. Then, the light beamemitted from the laser apparatus 10 passes through the irradiation unit20. Moreover, the light beam is changed in its angle by thebeam-irradiation-angle switching mirror 30, thereby being applied froman oblique direction to the semiconductor wafer 90 disposed on theinspection stage 80.

A scattered light of the light beam applied to the semiconductor wafer90 is captured into the beam-capturing camera 70 via the image-forminglens 50 and the beam-direction switching mirror 60, thereby beingrecognized as a foreign matter.

An automatic adjustment operation of the foreign-matter detectionsensitivity is automatically carried out immediately before carrying outthe above-described foreign-matter inspection operation. Hereinafter,the explanation will be given below concerning the automatic adjustmentoperation of the foreign-matter detection sensitivity.

FIG. 2 is a diagram for illustrating an optical portion of theirradiation unit 20. The diagram (A) in FIG. 2 illustrates a flat planethereof, (B) illustrates a side plane thereof, (C) illustrates a flatplane of a state where the optical portion is rotated from the state in(A), and (D) illustrates a side plane of the state in (C). The opticalportion includes two cylindrical lenses 20 c and 20 d and one raw glass20 e. The cylindrical lenses 20 c and 20 d are combined with each otherin a folding-fan shapes with the raw glass 20 e positioned therebetween.

The optical portion is not only rotatable as is indicated by an arrow 1,but also is movable in the up-and-down direction as is indicated by anarrow 2. The light beam emitted from the laser apparatus 10 passesthrough the optical portion as is indicated by an arrow 3. On account ofthis, rotating the optical portion as is indicated by the arrow 1 makesit possible to correct the inclination of the laser beam (i.e.,inclination of the ellipse-shaped beam's major axis or minor axisrelative to a constant reference line). Also, moving the optical portionin the up-and-down direction as is indicated by the arrow 2 makes itpossible to focus width of the laser beam. Here, the constant referenceline can be defined as a constant reference line on an image planephotographed by the beam-capturing camera 70.

FIG. 3 is an explanatory diagram for explaining the beam irradiationsample 40. In FIG. 3, the raw material of which the beam irradiationsample 40 is composed is alumina ceramic (aluminum-oxide ceramic), whichis low-cost, and is superior in abrasion-resistant property,heat-resistant property, and impact-resistant property. Moreover, beamirradiation surface of the beam irradiation sample 40 is polished sothat the surface diffusely reflects the laser beam.

The beam irradiation sample 40 is mounted to the inspection stage 80.The dimension of the beam irradiation sample 40 is, e.g., about 40 mm intransverse dimension Y, about 10 mm in longitudinal dimension X, andabout 10 mm in height dimension Z.

FIG. 4 is an operation-control functional block diagram of inclinationcorrection and focus correction for the laser beam. Incidentally, inthis operation-control functional block diagram, the mirrors 30 and 60and the inspection stage 80 illustrated in FIG. 1 are omitted.

In FIG. 4, the laser beam emitted from the laser apparatus 10 passesthrough the irradiation unit 20, then being applied to the beamirradiation sample 40. Moreover, the beam applied to the beamirradiation sample 40 is reflected by this beam irradiation sample 40,thereby being captured into the beam-capturing camera 70 via theimage-forming lens 50.

The beam image captured by the beam-capturing camera 70 is convertedinto an image file by an image-capturing board 71. Next, an imagecomputational processing unit (i.e., computational control unit) 72computes inclination correction amount and focus correction amount forthe laser beam. The inclination correction amount and focus correctionamount computed by the image computational processing unit 72 arerespectively supplied to a beam-inclination correcting motor driver 75 aand a beam-focus correcting motor driver 75 b via a motor-driverinterface 74.

The beam-inclination correcting motor driver 75 a activates abeam-inclination correction mechanism 20 a, thereby rotating the opticalportion illustrated in FIG. 2, and correcting the inclination of thelaser beam as was described above. Also, the beam-focus correcting motordriver 75 b activates a beam-focus correction mechanism 20 b, therebymoving the optical portion illustrated in FIG. 2 in the up-and-downdirection, and correcting the focus of the laser beam as was describedabove.

The laser beam whose inclination and focus have been corrected passesthrough the same route as the above-described one, then being suppliedinto the image-capturing board 71. Moreover, the laser beam is convertedinto the image file, then being image-displayed on a display 73 by theimage computational processing unit 72.

Incidentally, the image computational processing unit 72 is configuredwith a computer. In accordance with computer programs, the unit 72performs the laser-beam inclination correction and width correction ofthe irradiation unit 20. Also, the unit 72 performs operation controlsover the mirrors 30 and 60 and the inspection stage 80.

FIG. 5 is a flowchart (which is also available for flowchart forcomputer program) ranging from the beam irradiation to adjusting andsetting the beam inclination at an optimum value.

In FIG. 5, at the time of the detection-sensitivity automaticadjustment, the laser beam emitted from the laser apparatus 10 passesthrough the above-described route, then being applied to the beamirradiation sample 40. Next, the light beam is captured into thebeam-capturing camera 70 via the image-forming lens 50 and thebeam-direction switching mirror 60 (steps 201 and 202). Moreover, thecaptured beam image is stored into the file, and then the stored imagefile is divided in the X direction and is read by the imagecomputational processing unit 72 (steps 203 and 204). The divided andread data, which are luminance data, are quantified into numericalvalues. Furthermore, the image computational processing unit 72integrates the quantified data in the Y direction (step 205).

In addition, the image computational processing unit 72 applies asmoothing processing to the integrated data in order to eliminate noisecomponents from the integrated data (step 206). Then, the unit 72acquires Y coordinates each of which corresponds to a maximum value ofthe numerical values of the divided and smoothed data (step 207).Finally, the unit 72 plots, into a graph, the Y coordinates each ofwhich corresponds to the maximum value, then determining the inclinationfrom this graph (step 208).

FIG. 6A is a diagram for illustrating the beam image in the case wherethe transversely-long-ellipse-shaped laser beam is inclined. FIG. 6B isa diagram for illustrating the data on the Y coordinates of the maximumvalues of the divided and smoothed luminance values. In FIG. 6A, areference numeral 301 denotes the beam irradiation portion, and 300denotes a portion which is not irradiated with the beam. Also, 302denotes the Y axis (longitudinal axis) of the beam image, 303 denotesthe X axis (transverse axis) of the beam image, and 304 denotes the Ycoordinates of the maximum values at the time when the luminance valueswithin the width divided in the X direction are integrated in the Ydirection. A linear straight-line expression y=ax+b is determined fromthe graph illustrated in FIG. 6B, thereby calculating the inclination a(step 208).

At this time, if the inclination a falls within an apparatus-sensitivitytolerance range, no correction operation is executed, then terminatingthe operation flow (steps 209 and 211).

Meanwhile, if, at the step 209, the inclination a falls outside theapparatus-sensitivity tolerance range, the beam-inclination correctionmechanism 20 a is activated, then getting back to the step 202 (steps209 and 210).

FIG. 7A is a diagram for illustrating the beam after the beaminclination has been adjusted. FIG. 7B is a diagram for illustrating agraph of the maximum data on the luminance values after the beaminclination has been adjusted. In FIG. 7A, a reference numeral 401denotes the beam irradiation portion, and 400 denotes a portion which isnot irradiated with the beam. Also, 402 denotes the Y axis of the beamimage, 403 denotes the X axis of the beam image, and 404 denotes the Ycoordinates of the maximum values at the time when the luminance valueswithin the width divided in the X direction are integrated in the Ydirection.

As illustrated in FIG. 7A and FIG. 7B, it can be judged that the beaminclination has been corrected. FIG. 6A and FIG. 7A may be displayed onthe display 73 at the time of the detection-sensitivity adjustment.Otherwise, FIG. 6A and FIG. 7A may be displayed on the display 73 at thetime of the maintenance alone for confirming the beam inclination.

Next, the explanation will be given below concerning the focuscorrection for the laser beam. In this beam focus correction, the focusof the beam is automatically recognized, and is adjusted at a positionat which the beam is focused most. The position at which the beam isfocused most is a position at which the width of the beam is thenarrowest.

FIG. 8 is an operation flowchart for adjusting and setting the focusposition of the laser beam at an optimum value, i.e., thefocus-correction operation flowchart (which is also available forflowchart for computer program).

Steps 501 to 503 in FIG. 8 are basically the same operations as the onesat the steps 201 to 203 in FIG. 5. At a step 504, it is judged whetheror not the beam-image-captured number-of-times has attained to apredetermined value. If the beam-image-captured number-of-times has notattained to the predetermined value, the processing proceeds to a step505. At this step 505, the beam-focus correction mechanism 20 b isactivated by an arbitrary displacement amount, then getting back to thestep 502.

Meanwhile, if, at the step 504, the beam-image-captured number-of-timeshas attained to the predetermined value, the processing proceeds to astep 506, where the data are read from the stored image file. The readdata, which are luminance data, are quantified into numerical values(step 507). Moreover, the quantified data are integrated in the Ydirection, then being smoothed (step 508).

The maximum value of the integrated and smoothed data is determined(step 509). A value is determined which is equal to the one-half of themaximum value determined, then defining and employing this value as athreshold value (step 510). Furthermore, the distance between both endsof the luminance data attaining to the threshold value is defined as thewidth of the beam (step 511). The steps 506 to 511 are repeated untilall of the captured beam images have been processed (step 512).

A diagram (A) in FIG. 9 illustrates the beam width at the time ofdetermining the width of the beam. A diagram (B) in FIG. 9 is a graphindicating numerical value data on the beam width. A reference numeral601 denotes the beam irradiation portion, and 600 denotes a portionwhich is not irradiated with the beam. Also, 602 denotes the Y axis ofthe beam images, 603 denotes the X axis of the beam images, 604 denotesthe luminance value resulting from integrating the beam images in the Ydirection, and 605 denotes the one-half of the maximum luminance value.

From all of the captured beam images, a position of the beam-focuscorrection mechanism 20 b at which the beam width is the narrowest iscalculated. Then, the beam-focus correction mechanism 20 b is adjustedand set at the beam-focus correction mechanism coordinate at which thebeam width is the narrowest (steps 513 and 514).

FIG. 10 is a diagram for illustrating a screen 700 of a messagecharacter string 701 displayed on the display while carry-out of thesensitivity automatic adjustment is underway in the embodiment of thepresent invention. Also, FIG. 11 is a diagram for illustrating a screen800 of a message character string 801 displayed on the display when thesensitivity automatic adjustment is over in the embodiment of thepresent invention.

As illustrated in FIG. 10, the message 701 of “Now Adjusting asensitivity automatically” is displayed while execution of thesensitivity automatic adjustment is underway. As illustrated in FIG. 11,the message 801 of “Apparatus sensitivity is normal” is displayed whenthe sensitivity automatic adjustment is over normally. In FIG. 11, amessage of “Apparatus sensitivity is abnormal” is displayed at the timeof abnormality.

FIG. 12 is a diagram for illustrating a log file for recording thehistory which remains when the sensitivity automatic adjustment iscarried out in the embodiment of the present invention. Requirements tobe recorded in FIG. 12 are date 901, time 902, and a message 903indicating whether the termination when the sensitivity automaticadjustment is carried out is a normal termination or an abnormaltermination.

In the above-described example, either of the laser-beam inclinationcorrection and the laser-beam focus correction may be executed.Otherwise, both of them may be executed.

FIG. 13 is a diagram for illustrating a flowchart in the case where bothof the laser-beam inclination correction and the laser-beam focuscorrection are executed. In FIG. 13, the laser-beam inclinationcorrection illustrated in FIG. 5 is executed at a step 1000. After that,the laser-beam focus correction illustrated in FIG. 8 is executed at astep 1001.

When both of the laser-beam inclination correction and the laser-beamfocus correction are executed, as illustrated in FIG. 14, the laser-beamfocus correction (step 1001) is executed, and the laser-beam inclinationcorrection (step 1000) is executed. After that, the laser-beam focuscorrection (step 1002) may be executed once again in order to implementan enhancement in the accuracy.

As having been explained so far, according to the present invention, itbecomes possible to implement the foreign-matter inspection apparatus,foreign-matter inspection method, and computer program for theforeign-matter inspection apparatus which allows the stable detectionsensitivity to be maintained.

Namely, even if an imposition error occurs in the structure inside theforeign-matter inspection apparatus due to a reason such as time-lapsechange, the inclination and focus of the laser beam can be automaticallyadjusted and set into a constant state before the foreign-matterinspection operation. This feature makes it possible to prevent alowering in the foreign-matter detection sensitivity, thereby allowingthe stable detection sensitivity to be maintained.

Incidentally, the above-described embodiment is an embodiment in thecase where the present invention is applied to the foreign-matterinspection apparatus for detecting a foreign matter existing on asemiconductor-wafer surface. Not being limited to the semiconductorwafer, however, the present invention is also applicable to surfaceforeign-matter inspections in the other flat-plane-shaped inspectiontargets.

It should be further understood by those skilled in the art thatalthough the foregoing description has been made on embodiments of theinvention, the invention is not limited thereto and various changes andmodifications may be made without departing from the spirit of theinvention and the scope of the appended claims.

1-21. (canceled)
 22. An inspection apparatus comprising: a laser unitwhich irradiates laser; a beam irradiation sample which reflects laserfrom said laser unit; a beam capturing unit which captures a light fromsaid beam irradiation sample; a display unit which displays aninclination of said light.
 23. An inspection apparatus according toclaim 22, wherein said laser unit has plural lenses and a glass which isin between said plural lenses.
 24. An inspection apparatus according toclaim 22, wherein: said laser unit has at least beam inclinationcorrection mechanism or beam focus correction mechanism.
 25. Aninspection apparatus according to claim 22, wherein: said beamirradiation sample is aluminum oxide ceramic.
 26. An inspectionapparatus according to claim 22, wherein: said display unit displayssaid inclination of said light at the time of a detection sensitivityadjustment or maintenance.
 27. An inspection apparatus according toclaim 22, wherein: said display unit displays a history of a sensitivityadjustment.
 28. An inspection apparatus according to claim 27, wherein:said history includes at least date, or time, or message which indicatesnormal termination or an abnormal termination.